The present invention relates to a transfer bridge for letter sorting systems.
In prior art letter sorting systems, pieces of mail (particularly letters) are sorted, possibly after a presorting process, and deposited into a plurality of stack compartments or the like.
Such letter sorting systems are disclosed, for example in German patent document 2,008,521 and French patent document 7,003,430. Depending on the sorting process involved, the degree at which the sorting can be effected is determined by the number of stack compartments into which the mail is distributed. Particularly in the U.S. postal system, the items are to be sorted in the sequence in which the mail carrier distributes them during his rounds. For this purpose, in order to be able to work with a relatively small number of stack compartments, the mail is sorted several times as will be described in greater detail below. In the known, so-called sequencing process, to be described in greater detail below, it is possible to use a sorting system having ten stack compartments in three sorting passes, which represents a sequence of up to a thousand stops on the carrier route.
The sequencing of any desired number of mail items for eight hundred stops in a sorting system equipped with ten stack compartments and three sorting passes will be accomplished as follows:
The "stops" in the sequence are divided into eight successive groups of one hundred stops each. Each group is again subdivided into ten subgroups of ten stops each.
In the first sorting pass, the mail pieces assigned to stops 1 are deposited in the first stack compartment independently of whether a stop belongs to a group or a subgroup; pieces for stops 2 and 3 are deposited in the second and third stack compartments, respectively, and so on.
During the second sorting pass, the ten stack compartments are sequentially assigned to the ten subgroups. The pieces of mail assigned to stops 1 are sequentially distributed from the first stack compartment into the ten stack compartments depending on their subgroup, but independently of their association with a specific group. Then the mail pieces assigned to stops 2 from the second stack compartment are distributed to the ten stack compartments, etc.
During the third sorting pass, eight of the stack compartments are assigned sequentially to the eight groups. The mail pieces from the first stack compartment of the second sorting pass, which includes the ten stops from all first subgroups of all groups, are sorted sequentially corresponding to their group number. Then the second subgroups from the second stack compartment are sorted sequentially, etc.
In order to realize an economical progress in the three or more sorting passes, a letter sorting system disclosed in AEG brochure K2V37.6.216/1288, page 4, provides that the stack compartments are arranged opposite the material intake device so that, after each sorting pass that is to be followed by another sorting pass, the mail can be manually rapidly returned to the intake section from the stack compartments. For this purpose, the sorting system has an essentially U-shaped configuration in which one leg is formed by the material intake device and the other leg by the juxtaposed stack compartments.
A prerequisite for sequencing according to the above-described method is that the sequence integrity of the items, that is, the sequence of the items during the second and subsequent sorting passes and during the re-input, must be strictly maintained. However, when manually transferring the mail from the stack compartments to the intake device, there is a risk that the sequence integrity is lost if stacks of mail as a whole or in part are removed from the stack compartment by operating personnel and placed into the intake device. In order to overcome this problem, it is possible to use containers into which the mail pieces can be loaded after the initial sorting pass before being transported for re-input and unloaded into the intake device. However, the use of such containers can be complicated. Moreover, the risk has not been eliminated during loading and unloading of the stacks into and out of the containers that the sequence of the stacks is disturbed, either because items are pushed over one another, or because stacks are disarranged.